A power reception device and a power transmission device that transfer electric power in a contactless manner are known. Each of these devices includes a core and a coil wound around the core. As disclosed in PTD 1 described below, a coil having a round cross-sectional shape is generally used as the coil (coil wire). PTDs 2 and 3 described below disclose a litz wire having a round cross-sectional shape. This litz wire is formed by twisting a plurality of enamel wires or the like together.